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<title>pipe</title>
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<h2 align=center>pipe</h2>
<h4 align=center>OS/161 Reference Manual</h4>

<h3>Name</h3>
<p>
pipe - create pipe object
</p>

<h3>Library</h3>
<p>
Standard C Library (libc, -lc)
</p>

<h3>Synopsis</h3>
<p>
<tt>#include &lt;unistd.h&gt;</tt><br>
<br>
<tt>int</tt><br>
<tt>pipe(int *</tt><em>fds</em><tt>);</tt>
</p>

<h3>Description</h3>
<p>
The <tt>pipe</tt> call creates an anonymous pipe object in the system,
and binds it to two file handles in the current process, one for the
read end and one for the write end. (Pipes are unidirectional.)
</p>

<p>
Data written on the write end may be read from the read end. Once all
references to the write end are closed, and all remaining data is
read, further reads return EOF. If all references to the read end are
closed before the write end is closed, further writes generate EPIPE.
The pipe object itself is destroyed when all references to both ends
are closed.
</p>

<p>
<em>fds</em> is a pointer to space for two integers. A file handle for
the read end of the pipe is stored in <em>fds</em>[0], and a file
handle for the write end is stored in <em>fds</em>[1].
</p>

<p>
<tt>pipe</tt> is most often used in conjunction with <A
HREF=dup2.html>dup2</A> and <A HREF=fork.html>fork</A> to send the
standard output of one process to the standard input of another.
</p>

<p>
In POSIX, pipe I/O of data blocks smaller than a standard constant
PIPE_BUF is guaranteed to be atomic. If you implement pipes, you need
not necessarily implement POSIX semantics, but you should decide what
sort of atomicity guarantees you wish to make and specify them
carefully.
</p>

<h3>Return Values</h3>
<p>
On success, pipe returns 0. On error, -1 is returned, and
<A HREF=errno.html>errno</A> is set according to the error
encountered.
</p>

<h3>Errors</h3>
<p>
The following error codes should be returned under the conditions
given. Other error codes may be returned for other cases not
mentioned here.

<table width=90%>
<tr><td width=5% rowspan=3>&nbsp;</td>
    <td width=10% valign=top>EMFILE</td>
				<td>The process's file table was full, or a
				process-specific limit on open files
				was reached.</td></tr>
<tr><td valign=top>ENFILE</td>	<td>The system file table is full, if such a
				thing exists, or a system-wide limit
				on open files was reached.</td></tr>
<tr><td valign=top>EFAULT</td>	<td><em>fds</em> was an invalid
				pointer.</td></tr>
</table>
</p>

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